Compounds of the formula ab&#39;0.5 b&#34;0.5 o3 and process for preparing the same



States This invention relates to new and useful compounds possessing a perovskite structure.

Perovskite is a mineral having the chemical formula CaTiOg (calcium titanate). It is a crystalline material having a characteristic structure, and other crystalline materials having a similar type structure are often referred to as perovskite-type compounds. Crystals of the perovs'kite structure are represented by the general formula ABO' in which A is a divalent positive ion, and B is a tetravalent positive ion. The simplest perov skite crystal structure is a cube having one ABO formula per unit cell. In this structure, the A ions are at the corners of the unit cell, the B ion at the cell' center, the negative ions occupy the face-centered positions. Many investigators have studied crystalsexhibiting the perovskite structure and numerous perovskites with substitutions in the A and B sites have been reported. One of the earliest workers in this field was V. M. Goldschmidt who in 1926 reported (Skrifter Norske Videnshaps-Akad. Mat. Naturvid Kl. No. 2) the theoretical requirements and relationship for crystals of the perovskite structure. More recently, a comprehensive paper has been written by R. S. Roth (Journal of Research of the National Bureau of Standards, vol. 58, No. 2, Feburary 1957, Research Paper 2736). In his work, Roth discusses the A+ B+ O crystal structure of the perovskite-type crystal, as well as the A+ B+ O type structure. I. S. Waugh has reported (MIT Progress Report No. XXIII, p, 54 (1958)) perovskites with substitutions in the A-sites, such as La Ba MnO Those with substitutions in the B-sites such as LaZr Mg O have been reported by A. Rabenau (Z. anorg. Allgem. Chem. 288, 221-34 (1956)).

The perovskit'e-t'ype compounds of the present invention have the formula wherein A is a divalent alkaline earth metal ion selected from the group consisting of barium and strontium; B is a hexavalent metal ion selected from the group consisting of molybdenum and tungsten; and B" is a divalent metal ion selected from the group consisting of cobalt and nickel.

The compounds of this invention are prepared by firing a three-component, powdered mixture of (1) an alkaline earth metal compound selected from the group consisting of barium oxide, barium carbonate, strontium oxide, and strontium carbonate, (2) a group VI metal oxide selected from the group consisting of molybdenum oxide and tungsten oxide, and (3) a group VIII metal oxide selected from the group consisting of cobalt oxide and nickel oxide. a mixture are 2 mols of the alkaline earth metal compound and 1 mol of the group VI metal oxide and of the group VIII metal oxide. These amounts are the stoichiometric proportions for the reaction shown in the equation given below. It is preferred to use materials of the best available purity, and in instances where a transition metal oxide is being used in less than its maximum valence state, it is preferred to use and alkaline earth metal oxide rather than a carbonate. Firing temperatures usually range from The proportions of the components in such 1000 C. to 1400 C. The firing may be accomplished .of Example IL 3,034,853 Patented May 15, 1962 In a preferred procedure, the powdered mixture of reactants is prepared by grinding the reactants under acetone in a ball mill. mixture is fired vacuo at a temperature of from about l 000 C. to about 1200 C. for a period of from A2 to 2 hours. After regrinding and pressing, the resultant pellets are retired at a temperature of about 1300 C.-1400 C. for about 1 to 2 hours in vacuo. The product obtained is an A+ B+ O with substitution in the B-sites. These materials are useful as dielectric materials for capacitors and as ceramic materials. They are especially useful as a ceramic for electrical equipment.

As a result of the firing, chemical reaction takes place according to'Equation I when an alkaline earth metal carbonate is used, and according to Equation II when an alkaline earth metal oxide is used:

A, B, and B" represent the elements as heretofore disclosed, and C and 0 represent carbon and oxygen, respectively. For example, when A is strontium, B is tungsten, and B" is cobalt, the reaction proceeds according to Equation III when SrCOg is used, and according to Equation IV with SrO as a reactant:

. For a clearer understanding of the invention, the fol lowing specific examples are given. These examples are intended to be merely illustrative of the invention and not in limitation thereof. Unless otherwise specified, all parts are by weight.

EXAMPLE I A mixture was prepared comprising 10.00 g. of SrO and 6.93 g. of M00 and 3.58 g. NiO which are stoichiometric quantities of reactants for the equation:

The mixture was ground in an agate ball mill under acetone for 1 to 2 hours, filtered and dried. The mixture was fired in vacuum for about 2 hours at a temperature of 1200 C. The fired powder was remixed, this time dry, and waspressed into a pellet 1" in diameter using a pressure of 20,000 p.s.i. This pellet was then refired for 1 hour in vacuo. The ceramic polycrystalline pellet resulting was of about theoretical density.

The product was a crystalline material. Chemical analysis showed the material to contain 41.40% Sr, 23.07%, Mo, and 13.82% Ni. (The calculated values are 41.15% Sr, 22.53% Mo, 13.78% Ni.) X-ray diffraction analysis showed the crystalline material to be of distorted cubic structure having lattice parameter a =3.9237 and c =3.9474. The c/a ratio is 1.006. The electric properties are listed with data for other samples in the table EXAMPLE II Using the same general procedure as given in Example I, the compounds listed in the following table were prepared and tested by the procedures described below.

Theparameters of all cubic compounds were determined on the basis of powder diffraction patterns obtained in a 114.6 mm. Philips camera at 24.5 C. All films were corrected for film shrinkage and the parameters given can be considered as accurate to i0.0005 A. The parameters in crystals having a distorted cubic structure were obtained by use of a diffractometer.

The densities of the new compositions were determined by X-ray diiiraction methods and by means of pycno- After separation from the acetone, the" metric measurements. The densities were determined on powdered specimens of -200 mesh. For the pycnometric measurements, the samples were weighed into a 5 ml. pycnometer and C01 was distilled onto the sample under vacuum.

Resistivities were determined with an impedance bridge, and the dielectric constants were determined from capacitance measurements in disc-shaped samples of known dimensions at a frequency of one kiloeycle, using the relationship where C: capacitance K =dielectric constant 6 permittivity of free space, which is 885x10 farads/meter d: thickness of sample.

Any errors due to inaccuracies in measurement of the radius and thickness of sample are within the limits of experimental error in this art.

and strontium; B is selected from the group consisting of hexavalent tungsten and molybdenum; B is selected from the group consisting of divalent cobalt and nickel; and O is oxygen, which process comprises firing a powdered mixture of (1) an alkaline earth metal compound selected from the group consisting of barium oxide, barium carbonate, strontium oxide, and strontium carbonate; (2) a group VI metal oxide selected from the group consisting of molybdenum oxide and tungsten oxide; and (3) a group VIII metal oxide selected from the group consisting of cobalt oxide and nickel oxide, the proportions in said powdered mixture being 2 mols of the alkaline earth metal compound and 1 mol each of the group VI metal oxide and of the group VIII metal oxide.

2. A compound having the formula wherein A is selected from the group consisting of barium and strontium; B is selected from the group consisting of hexavalent tungsten and molybdenum; B" is selected from the group consisting of divalent cobalt and nickel; and O is oxygen.

Table Lattice Parameters Density Measure- 1 nits merits g.cc- Resis- Composition Chemical Analysis, Wt. Color Crystal Dielectric tivity.

percent Structure Constant ohm-cm.

0., co c/a X-Ray Pycnometric BaMou, Oon, O3.- Ba: 52.60 (52.27); Mo: 18.07 black cubic 4.0429 6. 60 6.48 4.64-

(18.25); Co 10.98 (11.21). Ba1\1oo 5Ni0 iO3. Ba 51.97 (52.29); Mo 18.76 Olive .d0 4.0225 6.70 6. 54 43.8 10

18.26); Ni: 10.93 (11.17). BaWo, Coo O3 Ba 43.64 (44.77); WV: 30.05 black d0 i. 4.050 7.67 7.51 0.34-10 (2999); Co: 9.71 (9.60). BaWo 5Nio O.1 Ba 44.12 (44.79); W: 28.88 light .d0 4.0326 7.76 7.59 12.7 10

(29 99) Ni: 9.93 (9.56). green SrM0o.5Nio.s0s S1: 1.15); M0: 23.07 11 Distorted 3. 9237 3. 9474 1.006 5. 82 5.90 1.4740 10 (22.53); Ni: 13.82 (13.78). cubic. SrMon.sCoo.s0a Sr;3Mo(: 22.367 (22.51); C0: black .do 3.9367 3.9764 1.01 5. 74 5.47 4.21-10 5.7140

1 .71 13.8 SrVVu.sCOo.s0a Sr: W: 34.93 (35.77); Co: dark ..do 3.9502 3.9746 1.006 6.46 6.51 8 65-10 1. 97-10 11.41 (11.46 brown SrW0 sNio,503 Sr; W: 34.86 (35.79); Ni: light do 3.9310 3. 9592 1.007 6. 97 6. 89 10.2 10

11.09 (11.42). green.

1 The number in parentheses in each case is the theoretical value for the compound.

The data given in the above table are considered to establish that the pro-ducts of this invention are new compositions of matter of the above formulae. Moreover, this table is significant from the standpoint of the electrical data set forth therein, particularly the high dielectric constants which render the materials useful in the manufacture of capacitors.

Since it is obvious that many changes and modifications can be made in the above-described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited to said details except as set forth in the appended claims.

I claim: 1. A process for producing a compound of the following formula wherein A is selected from the group consisting of barium References Cited in the file of this patent Hoffman: Lexikon der anorganischen Verbindungen, Band 11, pages 608, 611, 728, 724, and 729 (1912-1914). 

2. A COMPOUND HAVING THE FORMULA 